Third degree AV block laboratory findings

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Soroush Seifirad, M.D.[2] Raviteja Guddeti, M.B.B.S. [3]

Overview

Laboratory studies are warranted to diagnose etiologies of secondary heart block such as infections (either bacterial or viral), drug toxicity, and electrolyte abnormalities, and to screen for coincident problems that might either cause or exacerbate a previously presented compensated heart block.

Laboratory Findings

Class IIa

"1 Thyroid function tests, Lyme titer, potassium, pH) based on clinical suspicion for a potential underlying cause is recommended in patients with bradycardia (Level of Evidence C)"

There are plenty of diagnostic laboratory findings associated with third degree AV block. Laboratory studies are warranted to diagnose etiologies of secondary heart block such as infections (either bacterial or viral), drug toxicity, and electrolyte abnormalities, and to screen for coincident problems that might either cause or exacerbate a previously presented compensated heart block.

Primary lab work up of patients with third degree AV block might include but not limitted to the followings:

• Complete blood count - may reveal anemia (low RBC count), infection (leukocytosis is seen in myocarditis, acute rheumatic fever and viral infections)
• Differential count
• Serum electrolytes: Particularely hyperkalemia and magnesium spescially in selected patients such as those with renal insufficiency
• PT and aPTT may be ordered routinely
• Blood Digoxin levels should be measured in case of digoxin overdose
• Myocarditis related studies - HIV serologies, Lyme serology, Chagas serology, enterovirus PCR, adenovirus PCR
• Peripheral blood smears can aid in the diagnosis of hematological disorders like thalassemia major, Hodgkins lymphoma etc.,
• In patients with concerning history, toxicological studies for digoxin-like compounds such as:

• lily of the valley
• Oleander
• Foxglove
• Bufonidae toads

• Cardiac enzyme levels: if history or ECG findings are suggestive of active coronary artery disease.

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